1. Field of Invention
This invention relates to tissue resurfacing, for example, skin resurfacing, or the resurfacing or removal of tissue located within, e.g., the alimentary canal, respiratory tracts, blood vessels, uterus or urethra.
2. Description of Related Art
Human skin has two principal layers: the epidermis, which is the outer layer and typically has a thickness of around 120μ in the region of the face, and the dermis which is typically 20-30 times thicker than the epidermis, and contains hair follicles, sebaceous glands, nerve endings and fine blood capillaries. By volume the dermis is made up predominantly of the protein collagen.
A common aim of many cosmetic surgical procedures is to improve the appearance of a patient's skin. For example, a desirable clinical effect in the field of cosmetic surgery is to provide an improvement in the texture of ageing skin and to give it a more youthful appearance. These effects can be achieved by the removal of a part or all of the epidermis, and on occasions part of the dermis, causing the growth of a new epidermis having the desired properties. Additionally skin frequently contains scar tissue, the appearance of which is considered by some people to be detrimental to their attractiveness. The skin structure which gives rise to scar tissue is typically formed in the dermis. By removing the epidermis in a selected region and resculpting the scar tissue in the dermis it is possible to improve the appearance of certain types of scars, such as for example scars left by acne. The process of removing epidermal and possibly dermal tissue is known as skin resurfacing or dermabrasion.
One known technique for achieving skin resurfacing includes the mechanical removal of tissue by means of an abrasive wheel, for example. Another technique is known as a chemical peel, and involves the application of a corrosive chemical to the surface of the epidermis, to remove epidermal, and possibly dermal skin cells. Yet a further technique is laser resurfacing of the skin. Lasers are used to deliver a controlled amount of energy to the epidermis. This energy is absorbed by the epidermis causing necrosis of epidermal cells. Necrosis can occur either as a result of the energy absorption causing the temperature of the water in the cells to increase to a level at which the cells die, or alternatively, depending upon the frequency of the laser light employed, the energy may be absorbed by molecules within the cells of the epidermis in a manner which results in their dissociation. This molecular dissociation kills the cells, and as a side effect also gives rise to an increase in temperature of the skin.
Typically during laser resurfacing a laser beam is directed at a given treatment area of skin for a short period of time (typically less than one millisecond). This can be achieved either by pulsing the laser or by moving the laser continuously and sufficiently quickly that the beam is only incident upon a given area of skin for a predetermined period of time. A number of passes be may made over the skin surface, and dead skin debris is usually wiped from the skin between passes. Lasers currently employed for dermabrasion include a CO2 laser, and an Erbium-YAG laser. The mechanisms by which energy is absorbed by the tissue causing it to die, and the resultant clinical effects obtained, such as the depth of tissue necrosis and the magnitude of the thermal margin (i.e. the region surrounding the treated area that undergoes tissue modification as a result of absorbing heat) vary from one laser type to another. Essentially, however, the varying treatments provided by these lasers may be considered as a single type of treatment method in which a laser is used to impart energy to kill some or part of the epidermis (and depending upon the objective of the treatment, possibly part of the dermis), with the objective of creating growth of a new epidermis having an improved appearance, and also possibly the stimulation of new collagen growth in the dermis.
Other prior art references of background interest to the present invention include U.S. Pat. No. 3,699,967 (Anderson), U.S. Pat. No. 3,903,891 (Brayshaw), U.S. Pat. No. 4,040,426 (Morrison), U.S. Pat. No. 5,669,904, WO95/0759, WO95/26686 and WO98/35618.